Process and apparatus for reclamation of abrasive grit

ABSTRACT

A process for cleaning and reclaiming abrasive grit which includes the steps of initially scrubbing the grit with a liquid detergent, then separating relatively light impurities and residual detergent from the grit by flotation. The grit is then rinsed with clean water, and the rinsed grit is introduced to a heating zone which is heated to a temperature exceeding about 1000*F. In the heating zone, the grit is subjected to moving hot air currents and agitation, and particles of glass in the grit are agglomerated by fusion to relatively larger particles. Air current passed through the heating zone is directed to a cyclone where relatively fine particles of the grit are recovered. The apparatus in which the process of the invention is conducted includes a rotary vibrator screen for removing relatively dense particles of wood, metal and the like from the finer or smaller particles of abrasive grit, a whirlpool wash unit in which the abrasive grit is subjected to the cleaning action of a detergent, a pair of superimposed sequential washing rotary flotation tables, elevator means receiving abrasive grit from the lowermost rotary flotation table and an elongated low temperature furnace mounted for rotation about its longitudinal axis, and inclined with respect to the horizontal at an angle of between 5* and 15*. Finally, the apparatus includes means for moving air through the low temperature furnace, and a cyclone separator interposed in the air flow thus developed.

United States Patent [1 Jackson l l PROCESS AND APPARATUS FOR RECLAMATION OF ABRASIVE GRIT Edward L. Jackson, 2 [5 Terrace Dr, Pauls Valley, Okla. 73075 [22] Filed: Dec. 26, 1973 [2]] Appl No: 427,639

Related US. Application Data [62] Division of Ser. No, 204,420, Dec. 3, l97l, Pat. NO.

{76] Inventor:

Primary Exuminer-Frank W. Lutter Assistant Examiner-Ralph Jv Hill Attorney, Agent, or Firm--Laney, Dougherty, Hessin & Fish r i I08 //0 l l Sept. 16, 1975 [57] ABSTRACT A process for cleaning and reclaiming abrasive grit which includes the steps of initially scrubbing the grit with a liquid detergent, then separating relatively light impurities and residual detergent from the grit by flotation. The grit is then rinsed with clean water, and the rinsed grit is introduced to a heating zone which is heated to a temperature exceeding about 1000F. In the heating zone, the grit is subjected to moving hot air currents and agitation, and particles of glass in the grit are agglomerated by fusion to relatively larger particles. Air current passed through the heating zone is directed to a cyclone where relatively fine particles of the grit are recovered.

The apparatus in which the process of the invention is conducted includes a rotary vibrator screen for removing relatively dense particles of wood, metal and the like from the finer or smaller particles of abrasive grit, a whirlpool wash unit in which the abrasive grit is subjected to the cleaning action of a detergent, a pair of superimposed sequential washing rotary flotation tables, elevator means receiving abrasive grit from the lowermost rotary flotation table and an elongated low temperature furnace mounted for rotation about its longitudinal axis, and inclined with respect to the horizontal at an angle of between 5 and 15 Finally, the apparatus includes means for moving air through the low temperature furnace, and a cyclone separator interposed in the air flow thus developed 2 Claims, 4 Drawing Figures PATENTED SEP] 6 I975 snm 1 Of 2 mnu gmgmgnsmsms 3 905 898 sum 2 Bf 2 7 0000 000000000 OOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOQQQOOQO PROCESS AND APPARATUS FOR RECLAMA'IIUN ()F ABRASIVE GRIT RliLA'lliI) APPLICA'I IONS This application is a divisional application of US. Pat. application Ser. No. 204,420 entitled Process and Apparatus for Reclamation of Abrasive Grit filed Decv 3, 197], now US. Pat. No. 3,802,916.

BACKGROUND OF Tl-lli INVENTION I. Field of the Invention This invention relates to the cleaning and reclamation of spent abrasive grits ofthe type used for abrading and cleaning operations. More particularly, but not by way of limitation. the present invention relates to a method and apparatus for reclaiming aluminum coin-- pound-type abrasive particles after such particles have been utilized for abrading or cleaning various types of surfaces, and in particular, metal surfaces.

2. Brief Description of the Prior Art Various types of particles are used industrially for cleansing and polishing surfaces by abrasive action, or for abrading away surfaces to change the dimensions of various structural members. With some types of abrasive particles, a single usage destroys the abrasive prop erties of the particles so that they are no longer suitable for repeated usage in this way. Other types of particles do not suffer destruction of their abrasive characteristic in the manner described, and may be reutilized in the absence ofchemical change or physical contamina tion with impurities which impair their usefulness on the surfaces to be cleaned or polished upon reuse.

Among the abrasive grits in widespread industrial use which have the ability to retain their abrasive characteristic are the alummum-containing grits, including natural or synthetic alumina (aluminum oxide) and sili con carbide. These materials are widely used for cleaning and polishing operations, particularly in the aircraft industry, and are extremely hard and have high melting points. Alumina has a hexagonal crystalline structure, and its planes of cleavage are such that it fragments or fractures along these lines of cleavage in such a way that its cutting or abrasive properties are retained by the smaller particles developed upon fracturing.

In many industrial usages of aluminum oxide abrasive grit for cleaning and polishing, it becomes contaminated with particles of iron or steel, small particles of cellulosic material, such as paper or wood, moisture, grease and other foreign materials. In some industries, such the aircraft industry, the various abrasives used from time to time, such as glass beads, walnut shells and aluminum oxide, are recovered from a common situs of usage through the same ducting, etc., with the result that the spent alumina is contaminated with particles of glass, walnut shells, etc. It has been a widespread practice to discard the spent aluminum oxide abrasive grit. or at least to employ it for other utilizations than the original usage of cleaning and polishing. In the aircraft industry, certain standards of purity are required to characterize new aluminum oxide abrasive grit intended for certain cleaning and polishing usages. After utilization, the level of contamination with the described foreign materials and impurities is such that the grit is no longer suitable for the usage and does not meet the described standards. Discarding of this spent abrasive grit, or a substantial economic downgrading thereof as a result of such contamination results in a significant economic loss. While efforts have been made in the past to proce spent abrasive grit of this type to reduce the contamination thereof. no acceptable process for restoring the grit to the high level of purity of the fresh material has, to my knowledge, been developed,

BRIEF DESCRIPTION OF THE PRESENT INVENTION The present invention provides a method and apparatus for reclaiming contaminated abrasive grits or parti cles, and restoring them to a level of purity adequate for .heir reutilization in cleaning and polishing opera tions. The invention is particularly useful in restoring contaminated aluminum oxide abrasive grit which has been once used in metal cleaning and abrading opera tions to a level of purity substantially equivalent to that which characterized the g "t at the time of initial usage.

Broadly described, the .ocess of the invention comprises initially passing the contaminated grit through a physical classification device, such as a rotary screen, to remove from the grit relatively large particles of contaminants, and particularly, pieces of wood or other cellulosic material. The abrasive grit is then passed into a first cleaning zone where it is contacted, under agitation, with a liquid detergent which functions to remove dirt and grease adhered to or entrapped in the mass of grit particles. After the detergent cleaning action, the particles of grit are advanced to a first rotary flotation table where the abrasive particles are rinsed with water to remove detergent therefrom and undergo hydraulic particle separation to remove relatively light particles of foreign matter from the grit by flotation. The abrasive grit particles are then removed from the first rotary flotation table to a second rotary flotation table where the grit is subjected to a clean water rinse to remove residual detergent, and also any light, relatively less dense contaminants which may not be removed on the first table.

From the second rotary flotation table, the particles of abrasive grit are conveyed by suitable conveyor to a low temperature adhesion furnace. In the adhesion furnace, the particulate abrasive material is subjected to agitation, concurrently with heating to a temperature exceeding 300F, and preferably exceeding 400F. Simultaneously, a current of hot air is directed in a coun tercurrent fashion through the grit to remove moisture and very fine particles of the grit. The air current, moved through the furnace, is directed through a cyclone where any entrained very fine particles of grit are separated from any less dense materials carried in the air current. The heavy particles of grit and agglomerated particles of glass are then removed from the grit by particle size classification, such as by screening. Finally, if contamination with fine particles of ferrous metals is involved, magnetic particle separation may be utilized for removing the magnetic particles from the nonmagnetic particles of grit.

It is an object of the present invention to reclaim abrasive grit by restoring it to a condition suitable for industrial cleaning and abrasive usages in which low contamination of the grit is required.

Another, and more specific, object of the invention is to remove grease, cellulosic and glassy contaminants from metallic abrasive particles.

Another object of the invention is to reclaim spent aluminum oxide abrasive particles by the efficient removal of various contaminants therefrom.

Another object of the invention is to reclaim alumina abrasive grit by the removal of various contaminating materials therefrom, and in the course of such reclamation, to effect a desirable classification of the grit on the basis of particle size so that selective usage of the classified particles may be readily practiced.

Additional objects and advantages of the invention will become apparent as the following detailed descrip tion of the invention is read in conjunction with the accompanying drawings which illustate the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a partially schematic illustration of one embodiment of the apparatus and system utilized in reclaiming abrasive grit in accordance with the process of the present invention.

FIG. 2 is a sectional view taken along line 2-2 of FIG. 1.

FIG. 3 is a sectional view taken along line 3-3 of FIG. 1 and showing details of the rotary vibrator screen used in the invention.

FIG. 4 is a sectional view taken along line 44 of FIG. 1.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION In FIG. 1 of the drawings, a hopper for receiving spent or contaminated abrasive grit in a relatively dry state from a chute I2 is illustrated. A second chute I4 is used for delivering moist or wet contaminated abrasive grit to the system of the invention. From the dry grit hopper 10, the grit is passed through a suitable metering valve 16 to a conveyor 18. The conveyor 18 moves the relatively dry, contaminated abrasive grit into a hood 20 which serves to confine airborne fines of very light weight which are stirred up by the agitation of the conveyor and a screening device subsequently used in the process, and to permit these airborne fines to be drawn off or ducted through a duct 22 and conveyed thereby into a suitable cyclone 24 to collect these fines and discharge them through a suitable valve 26 to a point subsequently in the process as hereinafter described.

Within the hood 20 is located a rotary vibrator screen assembly designated generally by reference numeral 28. The rotary vibrator screen assembly 28 includes a framework which carries an internal screen 32 of frustoconical configuration and having openings therethrough of about A inch in diameter. An external or outer screen 34 is supported on the framework and extends concentrically around the inner screen 32. The outer screen 34 is characterized in having openings therethrough of about 3/32 inch in diameter. At its end opposite the end into which the conveyor 18 projects, the rotary vibrator screen 28 includes an open-ended cylindrical metallic portion 36 which receives the overage from the screens 32 and 34. A yieldable, spring loaded vibrator arm 38 extends into the open end of the metallic portion 36 and yieldingly contacts the vanes of a spider 40 (see FIGS. 3 and 4). The overage from the vibrator screen 28 enters a chute 42 which discharges into a suitable waste hopper 44.

In the operation of the rotary vibrator screen 28, the dry abrasive grit is received in this screen which is continuously driven in rotation by a suitable electric motor 46, and the dry abrasive grit is moved slowly by gravity towards the relatively large end of the rotary vibrator screen assembly 28. In the course of this movement, an initial screening action is performed by the internal screen 32, and a final screening action by the external screen 34. The internal screen helps to prevent clogging or choking of the external screen by screening from the mass of relatively dry abrasive grit, relatively large particles of cellulosic materials, such as wood chips, sawdust, paper particles and the like. This over age of contaminant materials enters the large end of the rotary vibrator screen assembly 28 and is removed from this location by the chute 42 to the waste hopper 44. The arm 38 periodically striking the vanes of the spider 40 vibrates the assembly and the material passing therethrough to prevent balling" or aggolmeration of the material, and to aid in preventing clogging of the screens.

The abrasive grit which passes through the screens 32 and 34 is passed into a whirlpool wash unit 48. The whirlpool wash unit has a generally cylindrical upper portion and a frustoconical lower portion which communicates with a chute containing a metering valve 50. Wash water is conveyed to the central portion of the whirlpool wash unit 48 by a suitable wash water conduit 52. Before the wash water enters the whirlpool wash unit 48, liquid detergent is injected into the wash water stream from a suitable conduit 54. The amount of detergent introduced to the stream of wash water is controlled by a suitable valve 56. Within the whirlpool wash unit 48, the aqueous detergent solution is constantly agitated by a stirrer 58 driven by a motor 60. The stirrer 58 is constructed and oriented in the whirL pool wash unit 48 so as to cause currents of the detergent solution to circulate in a vertical direction inside the wash unit.

In addition to the relatively dry abrasive grit which enters the whirlpool wash unit 48 from the rotary vibrator screen assembly 28, damp or wet abrasive grit which has been dampened during prior use may also be introduced to the wash unit 48 through the pipe 14. This material cannot be subjected to the rotary screening process because of its propensity to choke or clog the screen. Moreover. in many industrial processes in use, the wet abrasive grit will not contain the high level of cellulosic contaminants which characterize the dry abrasive grit, and thus this material can be more easily passed to the whirlpool wash unit without prior screening than can the dry abrasive grit.

Within the whirlpool wash unit 48, the abrasive grit is subjected to a whirling lifting action in which it is lifted up from the center of the conical bottom toward the top of the unit and is propelled then by centrifugal force of the whirlpool created in the unit outwardly toward the confining walls of the unit. It then descends along these walls to the conical bottom. The flow out of the whirlpool wash unit 48 is metered by adjustment of the metering valve 50. A float 51 senses the level of liquid in the unit 48 and controls the degree of closure of solenoid valve 56 to maintain a constant desired liquid level in the unit. It may be noted that many abrasive grits, such as alumina, have relatively high specific gravities. In the case of alumina. the average specific gravity is about 4.0.

The abrasive grit from the whirlpool wash unit 48 is discharged through the metering valve 50 on to the apex of a conical member carried by, and forming a part of, a rotary flotation table assembly designated generally by reference numeral 64. As shown in FIGS. 1 and 2. the rotary flotation table assembly 64 includes a round table 66 having the cone 68 secured in a central position thereon for rotation therewith. At its outer peripheral edge, the table 66 has a vertically extending annular lip 70 which projects upwardly, In the illus trated embodiment of the invention, the lip 70 is 2 inches in height. The table has a diameter of 36 inches, and the cone is 24 inches in diameter at its basev The table 66 is mounted on a supporting plate 72 which is driven in rotation by a suitable shaft 74 secured thereto at a central point. The shaft 74 is driven in rotation by a drive chain 76 engaging a sprocket 78 keyed to the lower end of this shaft. The chain 76 is driven by a suitable motor 80 which is also used to drive another rotary flotation table assembly as hereinafter described.

The rotary flotation table 66 is positioned in an open topped overflow tank 82 which has an inclined bottom permitting the tank to discharge through a pipe 84. As the detergent solution containing washed abrasive grit is discharged from the whirlpool wash unit 48 onto the apex of the cone 68 forming a portion of the rotary flotation table assembly 64, the detergent solution, of course. fills the volume defined inside the lip 70 of the rotary table and overflows this lip. The rotation of the table, coupled with the spreading effect of the cone 68 causes the solid particulate material including the abrasive grit to be moved radially outwardly toward the peripheral edge of the table 66. The relatively more dense material, including the abrasive grit particles and particles of metal and glass, deposit on the table after sinking downwardly through the detergent solution. The less dense, flotable materials move to the surface of the liquid. and flow over the top of the lip 70 and fall downwardly with the solution into the overflow tank 82. From the overflow tank 82, detergent solution contain ing light contaminant materials flows through the pipe 84 to a suitable filtering system (not shown) where the solid contaminants are removed from the detergent solution. The detergent solution is then recycled to the pipe 54 for introduction again to the whirlpool wash unit 48.

The abrasive grit which has been deposited on the upper surface of the table 66 beneath the surface of the liquid carried thereon is moved outwardly toward the peripheral edge of the table by the centrifugal force acting as the table is slowly rotated. Also deposited on the outer peripheral portion of the table 66 are abrasive grit particles from the cyclone 24. Projecting downwardly into contact with the table 66 is a chute 86 of L-shaped cross section. The chute 86 has a small bend therein to permit it to clear the peripheral lip 70 of the rotary flotation table assembly 64, and then has a downwardly inclined portion 86a which extends to a manifold 104 positioned over a second rotary flotation table assembly 90.

It will be noted in referring to P10. 2 that the chute 86 opens onto the table 66 so that, as the table 66 is rotated in a counterclockwise direction as viewed in FIG.

2, abrasive grit carried on the table tends to be moved into the open end of the chute. To aid in the movement of the abrasive grit onto the chute 86 and over the angulation therein, a pipe 89 having downwardly projecting perforations formed therein extends over the table 66 and a portion of the chute 86 and from these perforations. jets of water play upon the table and the chute in a direction to force abrasive grit onto the chute and over the angulation in the chute formed for the purpose of clearing the lip 70.

A second rotary flotation table assembly 90 is constructed somewhat similarly to the rotary flotation table assembly 64. It thus includes a conical member 92 mounted centrally upon a flat, horizontally extending table 94 which is driven in rotation by a shaft 96 se cured centrally to the lower side thereof. The shaft carries a sprocket 98 which is engaged by the chain 76 hereinbefore described. The sprocket 98 is of the same size as the sprocket 78 used for driving the rotary flotation table assembly 64 so that the tables 66 and 94 are driven at equal speeds of rotation. The dimensions of the tables 66 and 94 are the samev At its outer periphery, the table 94 carries an annular lip 100 which is about 4 inches in height in a preferred embodiment of the invention, and thus has twice the vertical dimension of the annular lip surrounding the rotary table 66. The rotary flotation table assembly further includes an overflow tank 102 which receives liquid flowing over the lip from the table 94. The bottom of the overflow tank 102 in inclined so as to permit the con tents of the tank to drain through a discharge conduit [03 into a collection tank 105. From the collection tank 105, very small fines of abrasive grit (referred to as hydraulic fines of flour) are removed from the rinse Water and are recycled to the top of the table 94 by any suitable means.

For the purpose of conveying the abrasive grit from the chute 86 onto the table 94 of the second rotary flotation table assembly 90, the chute 86 has its discharge end connected to an annular manifold 104 which receives the grit and discharges it through an arcuate opening 106 formed in one side of the manifold. The grit and water in which it is carried gravitates down one side of the cone 92 onto the table 94. The cone 92 is continuously washed clean and water is supplied to the space enclosed by the lip 100 by means of an annular wash ring 108 having perforations in the lower side thereof which direct water downwardly onto the cone 92. The wash ring 108 may suitably be mounted around the manifold 104 as depicted in FIGS. 1 and 2.

Extending over the edge of the lip 100 and into close proximity to the upper surface of the table 94 is a drag elevator assembly, designated generally by reference numeral 110. The drag elevator assembly 110 includes an endless belt or chain 112 which carries thereon a plurality of outwardly projecting teeth 114. The endless belt or chain 112 passes over a drive roller 116 and a pair of idler rollers 118 and 120. It will be noted in referring to FIGS. 1 and 2 that the teeth 114 of the drag elevator assembly 110 pass in close proximity to the upper surface of the table 94 and are oriented so that these teeth will pick up and carry upwardly on the drag elevator assembly, the accumulated particles of abrasive grit which are moved against the lower end of the drag elevator assembly by the rotating table 94. It will be noted in referring to FIG. 2 that the discharge opening 106 in the manifold 104 is oriented with respect to the lower end of the drag elevator assembly 110 so that abrasive grit is discharged down the side of the cone 92 onto a portion of the table 94 which, considering the direction of rotation of the table, has furthest to travel before arriving at the pickup end of the drag elevator assembly. This affords maximum opportunity for washing of the particles of abrasive grit before being deposited against the drag elevator assembly and picked up by the teeth 114 thereof.

Abrasive grit falls from the upper end of the drag ele' vator assembly 110 onto a slide I24 and moves down the slide into a low temperature rotary furnace assembly designated generally by reference numeral I26. The low temperature rotary furnace assembly 126 includes a cylindrical furnace housing I28 which is mounted with its longitudinal axis extending at an angle of between and I5 with respect to the horizontal, and preferably at an angle of about 8 to the horizontal. The furnace housing 128 is supported in suitable bearings or trunions I30 and 132, and is driven in rotation about its longitudinal axis by a suitable motor I34. The motor 134 drives a gear I36 which meshes with an annular gear ring I38 carried by the cylindrical housing I28. A plurality of axially extending. circumferentially spaced mixer flights I39 are secured around the internal wall of the cylindrical housing 128.

At its upper end, the furnace housing 128 opens into a hood I40 which is vented through a duct 142 to the upper end of a cyclone I44. The overhead discharge from the cyclone 144 is passed through a filter element 146 and is drawn through a suction fan I48 driven by a motor I50. The suction fan I48 discharges to the atmosphere. At its lower end, the furnace housing I28 opens into a hood I52 in which is mounted a blower burner assembly 154 which directs a jet of flame into the discharge end of the furnace housing I28, and which also cooperates with the suction fan I48 creating a significant air fow through the furnace housing. Material discharged from the lower end of the furnace housing 128 passes through an opening in the lower portion of the hood I52 and gravitates into a cooling drum 158 where the abrasive grit and other material discharged from the furnace is cooled.

OPERATION In the operation of the apparatus referred to in the description of FIG. I, spent abrasive grit in a relatively dry state is introduced to the process of the invention via the chute 12. From the hopper I0, the dry grit is discharged onto the conveyor 18 which moves the relatively dry grit into the rotary screen assembly 28 located in the hood 20. Airborne fines in the hood are removed through the duct 22 to the cyclone 24 where they are taken out of the air and directed through a suitable pipe 27 to the table 66 forming a portion of the first rotary flotation table assembly 64.

In the rotary vibrator screen assembly 28, relatively large particles of paper, pieces of wood, chunks of metal, walnut shell particles (sometimes mixed with the grit for cleaning operations) and the like are screened from the abrasive grit and are passed out of the screen assembly onto a chute 42 which delivers these foreign materials to a waste hopper 44. The screened grit passes from the rotary screen assembly 28 into the whirlpool wash unit 48. Here the grit is subjected to intense agitation and contact with a detergent solution. The detergent utilized is a strong surfactant material added to the incoming wash water via the conduit 54. Wet or damp abrasive grit may also be introduced to the whirlpool wash unit 48 from the pipe 14.

In the whirlpool wash unit. the detergency action of the detergent solution scrubs the grit and removes grease, hydrocarbons and dirt therefrom. and entrains this in the detergent solution. The grit eventually accumulates in the frustoconical lower end of the whirlpool wash unit 48 and is discharged therefrom by the meter; ing valve IS. The abrasive grit and detergent solution are discharged from the whirlpool wash unit at a metered rate which corresponds to the rate at which fresh detergent solution and contaminated abrasive grit are being introduced to this unit. so that the level of material in the unit remains substantially constant.

Abrasive grit and detergent solution are deposited upon the table 66 of the rotary flotation table assembly 64 typically at a rate of about 50 gallons per minute. With such deposition, the grit sinks to the bottom of the solution and rests upon the table. and detergent solu tion carrying grease and dirt removed from the grit floats over the top of lip 70 and falls downwardly into the overflow tank 82. The contaminated spent deter gent solution is then discharged through the pipe 84.

Abrasive grit tends to move outwardly on the table 66 and to accumulate toward the outer peripheral edge thereof. From this location, it is scooped up by the open end of the chute 86 and is moved into the chute by the jets of water directed downwardly from the pipe 89. The abrasive grit is washed down the downwardly inclined portion 86a of the chute 86, passes through the manifold I04, and is discharged through the opening formed on one side of the manifold at a location on one side of the cone 92. From this location, the grit is deposited upon the rotary table 94 at a locus which is se iected to permit the grit to move through the major portion of one full rotation of the table before arriving at the point where the grit is picked up by the drag elevator assembly I10.

On the table 94, the grit is further washed by water jetted downwardly on the table from the annular wash ring 108, and this water also functions to clean the surface of the cone 92. The function of the rotary flotation table assembly is to dilute residual detergent solution carried onto the table by the abrasive grit. and to remove this detergent solution from the grit. Actually, some very small abrasive grit particles are caused to wash over the lip (which extends around the pe riphery of the table 94) into the overflow tank 102 and to be discharged from this tank into the collection tank 106. These so-called hydraulic fines are then recovered and recirculated to the table 94 so as to be retained in the process stream. Usually, less than about 0.5 weight percent of the total abrasive grit on the table 94 will be recycled in this way. The detergent solution, after separation of the hydraulic fines therefrom. can be returned to the feed to the whirlpool wash unit 48.

As abrasive grit accumulates on the table 94, it is picked up by the drag elevator assembly and car ried upwardly thereby and deposited in the low temperature rotary furnace assembly I26. During this upward movement, water is drained from the abrasive grit. The function of this furnace assembly in the process of the present invention is an important one. In the furnace. the temperature is elevated to above I000F, and preferably to between about I200F and I300F. Concurrently. hot air currents move through the rotary fur nace in a direction which is countercurrent with respect to the direction of movement of the abrasive grit through the furnace. The abrasive grit is thus subjected to elevated temperatures such that combustible contaminants which may still be entrained in the grit are bumed and convened to light ash materials or gasses which can be entrained in the air currents moving through the furnace.

An additional function is that small flakes of metallic contaminants are oxidized to metallic oxides of lesser specific gravity. and may thus be entrained in the air currents flowing through the furnace.

Another important function of the furnace is to effect the agglomeration of particles of glassy vitreous contaminants. It is not uncommon for the abrasive grit to be contaminated with very fine particles ofglass. At the temperatures prevailing in the rotary furnace assembly 126, the outer peripheral portions of the small particles of glass are softened or plasticized by the elevated temperatures, and the result is that the particles of glass tend to fuse with each other and agglomerate to form relatively large particles of glass. The average particle size of these agglomerated glass particles is larger than the average particle size of the abrasive grit, thus facilitating subsequent separation by screening. The abrasive grit, on the other hand, is usually a material which does not undergo such agglomeration, since it has a much higher melting point and is generally present, for the most part, in larger particles than the very fine glass, and is more dense than the glass, and is thus not held up by or entrained in the hot combustion gases as are the glass particles. Moreover, the residual moisture in the mass of denser, larger abrasive grit particles tends to cool these particles so that they emerge from the furnace at a relatively cool temperature in general at about 400F.

A final function of the low temperature rotary furnace assembly 126 is to remove entrained moisture from the abrasive grit. Thus, the moisture is evaporated and passes with the hot air currents through the duct 142 to the cyclone 144. Here, a final separation is effected to again pick up any very light, extremely fine or small particles of abrasive grit (less than about 42 mi crons in diameter). These are removed in the cyclone I44 and recovered as an abrasive grit fraction of very small particle size. Abrasive grit of this size has many special usages, and for this reason, is an especially valuable fraction of the grit. The air stream delivering the fine particles of abrasive grit to the cyclone 144 is then passed through a filter 146 where any entrained light materials not removed by the cyclone 144 are removed. The relatively clean air stream is discharged to the atmosphere.

From the low temperature rotary furnace assembly 126, abrasive grit and the agglomerated silica particles, along with any entrained particles of ferrous metal which may be present as a contaminant, are discharged from the furnace housing 128 into the cooling drum 158. The material as thus recovered from the furnace assembly 126 may then be subjected to magnetic separation to remove ferrous metals from the abrasive grit, and to screening to remove the relatively large agglomerated particles of silica from the smaller particles of abrasive grit.

The described process and apparatus for reclaiming abrasive grit has proven to be a highly efficient procedure for restoring abrasive grit, and particularly alumi- (ill num oxide, to the state of purity which characterizes this material prior to initia i use. The highest industrial standards of purity for St .h grits can be met by the product of the process of the invention. After cleaning and regrading the material, it is suitable for usage in grinding and lapping compounds, wet honing compositions, mounted grinding stones and wheels, and substantially all other uses to which the original material may be put.

Although a preferred embodiment of the invention has been herein described in order to illustrate the prin ciples of the invention sufficiently for those skilled in the art to practice the invention, it will be understood that various changes and modifications in the described apparatus and process steps can be effected without departure from these principles. Changes and innovations of this type are therefore deemed to be circumscribed by the spirit and scope of the invention, except as the same may be necessari limited by the appended claims or reasonable equivalents thereof.

What is claimed is:

l. A separatory device for hydraulically separating abrasive grit materials comprising:

a flotation table having an upwardly facing surface;

a cone positioned centrally on said flotation table and having its apex centered over said table;

a peripheral lip secured to the outer periphery of said table and projecting upwardly therefrom for con fining liquid on said table to a certain depth;

a chute of U-shaped cross section having an open intake end immediately adjacent the upwardly facing surface of said table inside said lip and extending upwardly therefrom over said lip and thence downwardly from said lip;

downwardly directed fluid jet means positioned adjacent and over the open intake end of said chute for moving material from said table into and up said chute; and

means for rotating said table, cone and peripheral lip.

2. A separatory device as defined in claim 1 and further characterized as including a second flotation table positioned at a lower level than said first flotation table and having an upwardly facing surface;

a cone positioned centrally on said second flotation table and having its apex centered over said table;

a peripheral lip secured to the outer periphery of said second flotation table and projecting upwardly therefrom for confining liquid on said table to a certain depth;

a manifold positioned over said second flotation table and connected to said chute for receiving solid materials and water from said chute;

an annular pipe having downwardly opening perforations therein for directing jets of water downwardly onto the cone positioned on said second flotation table; and

means for rotating said second flotation table, the cone positioned thereon, and the peripheral lip car ried thereby. 

1. A SEPARATORY DEVICE FOR HYDRAULICALLY SEPARATNG ABRASIVE GRIT MATERIALS COMPOSING: A FLOTATION TABLE HAVING AN UPWARDLY FACING SURFACE: A CONE POSITIONED CENTALLY ON SAID FLOTATION TABLE AND HAVING ITS APEX CENTERED SAID TABLE: A PERIPHERAL LIP SECURED TO THE OUTER PERIPHERY OF SAID TABLE AND PROJECTING UPWARDLY THEREFROM FOR CONFINING LIQUID ON SAID TABLE TO A CERTAIN DEPTH:: A CHUTE OF U-SHAPED CROSS SECTION HAVING AN OPEN INTAKE END IMMEDIATELY ADJACENT THE UPWARDLY FACING SURFACE OF SAID TABLE INSIDE SAID LIP AND EXTENDING UPWARDLY THEREFROM OVER SAID LIP AND THENCE DOWNWARDLY FROM SAID LIP: DOWNWARDLY DIRECTED FLUID JET MEANS POSITIONED ADJACENT AND OVER THE OPEN INTAKE END OF SAID CHUTE FOR MOVING MATERIAL FROM SAID TABLE INTO AND UP SAID CHUTE: AND MEANS FOR ROTATING SAID TABLE, CONE AND PERIPHERAL LIP.
 2. A separatory device as defined in claim 1 and further characterized as including a second flotation table positioned at a lower level than said first flotation table and having an upwardly facing surface; a cone positioned centrally on said second flotation table and having its apex centered over said table; a peripheral lip secured to the outer periphery of said second flotation table and projecting upwardly therefrom for confining liquid on said table to a certain depth; a manifold positioned over said second flotation table and connected to said chute for receiving solid materials and water from said chute; an annular pipe having downwardly opening perforations therein for directing jets of water downwardly onto the cone positioned on said second fLotation table; and means for rotating said second flotation table, the cone positioned thereon, and the peripheral lip carried thereby. 